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What Effects do Forest Fires have on the Storage of Carbon?

By Tania Peñafort

Forests and the Global Carbon Cycle

Carbon dioxide in the atmosphere has been increasing steadily since at least 1958. Predictions of future climate change as a consequence of increasing atmospheric carbon dioxide vary widely. Under a scenario of equivalent doubling of atmospheric carbon dioxide by the middle of the next century, most predictions show an increase in average global temperature, between 2 and 5 degrees centigrade, and an increase in average global precipitation of between 7 and 15 percent (Jones et al., 1990). These prospective changes have generated interest in strategies to reduce emissions of carbon dioxide to the atmosphere, or to offset emissions by storing additional carbon in forests.

A key issue analyzed in the 1989 Resources Planning Act (RPA) Assessment is the impact of climate change on America's forests (Birdsey, 1992). Another issue undergoing intense analysis at this time but not included in the 1989 RPA Assessment, is the evaluation of forests mitigating the effects of global warming. Analysis of this proposition requires knowledge of carbon storage and accumulation in forest ecosystems.

Forest ecosystems are capable of storing large quantities of carbon in trees, other organic matter, and soil. Forests may add to the pool of carbon dioxide in the atmosphere through deforestation, decomposition of wood products and byproducts, or burning of forest lands. Forests may also reduce the amount of carbon dioxide in the atmosphere through increases in biomass and organic matter accumulation. Because of the relation between forests and atmospheric carbon dioxide, there are opportunities to manage forests in ways that would result in storage of additional carbon and thus reduce atmospheric carbon dioxide. These include increasing forest area, increasing the productivity of existing forest lands, reducing forest burning and deforestation, and planting trees in urban environments.

Encarta defines forest fires as natural or human caused fires that burn vegetation. Most forest fires result from human carelessness while lightning starts other fires. Weather conditions influence the susceptibility of an area to fire; such factors as temperature, humidity, and rainfall determine the rate and extent to which flammable material dries and, hence, the burning of the forest. Wind movement also tends to accelerate drying and to increase the severity of fires by speeding up combustion.

Although organizations involved with fire control have traditionally fought all fires, certain fires are a natural part of an ecosystem. Complete fire exclusion may bring about changes in vegetation patterns and may also allow accumulation of fuel, with increased potential for feeding catastrophic fires. In addition, forest fires may:

Reduce the build-up of fuel, and thus the intensity of future burns.

Recycle nutrients bound up in litter.

Reduce competition, allowing existing trees to grow larger.

Leave snags that provide nesting spots for woodpeckers and other birds.

Sprout seeds of native plants. For example, the cones of many lodge pole pines -- the characteristic tree of Yellowstone -- will only open after exposure to fire.

Kill non-native plants that are not adapted to fire.

Another concept of forest fires is that they are often set deliberately to clear forested areas for grazing or agricultural purposes. In slash-and-burn cultivation, subsistence farmers burn small plots of forest for space to grow crops. After two or three years, when the nutrients in the soil have been depleted, the plots are abandoned and other plots are cleared by fire. Large-scale agricultural operations use similar methods to clear-forested areas. These practices, along with logging operations, destroyed much of the world's tropical rain forests during the 1980s and 1990s. The El Niño weather pattern of 1997-1998 disrupted rainfall patterns, leaving many forests dry. Thousands of deliberately set forest fires raged out of control in Indonesia, Brazil, and Mexico, burning millions of hectares of rain forest. Thick clouds of smoke blanketed vast areas in Southeast Asia, South America, and Central America, sending tens of thousands of people to hospitals with respiratory illnesses related to the air pollution. Inevitability forest fires are quandaries. (Encarta)

To better understand the role that a forest ecosystem has on the storage of carbon, a study will be conducted to analyze the effects that a forest fire has on the storage of carbon. Several experimental techniques and protocols have been used to determine the amount of carbon stored in a burned part of an eastern forest (experimental variable) compared to an unburned area (control). It is imperative that the importance of this research is understood. Through enhanced understandings of carbon, could this study contribute to our growing knowledge of climate and therefore to the production of climate models?

The forest that now occupies the Hudson Highlands first developed nearly 15,000 years ago. Located in Cornwall New York, Black Rock Forest was the home of European settlers and Native Americans in the 1700ís. In 1949 the owner of the forest, Ernest Stillman, passed away and left the Black Rock Forest to Harvard University. Since then it has been a center for scientific research and education. Black Rock Forest provided the sites for the carbon storage study. Black Rock Forest is a good place to study because it is an exceptional representation of eastern forests.

The two sites originally were equivalent in tree species, diversity, elevation and topography. The unburned site is a moderately moist type ecosystem consisting of mostly red and chestnut oak trees. Blue berry bushes cover the forest floor and small amounts of red maple and which hazel also are parts of the siteís biodiversity.

There have been four fires in the last 15 years. All were man made. If fire is a regular feature of the plant atmosphere, plants usually have special adaptations to render them fire resistant. (Collinson, 1988) In this case, fire is not a regular feature. The burned site was the result of an uncontrolled campfire that turned into a ground fire four years ago. As a result, all of the ground level vegetation and suppressed trees were burned or destroyed, minimizing the siteís biodiversity.

The hypothesis that has been created for this study states that the unburned site will significantly store more carbon than the burned site. Other research has concluded that when something is burned, the carbon stored in it is released. When we burn wood, coal and petroleum products we are releasing the sunís energy that was trapped long ago by photosynthesis. (Kraus, Concepts in Modern Biology)

As glucose is burned, it oxidizes creating a new gas called carbon dioxide (CO2). Photosynthesis on land -- most of which is accomplished by the leaves and needles of trees -- removes CO2 from the atmosphere at the prodigious rate of about 60 Gt. C/yr., worldwide (Kasting, 1996) and simultaneously stores carbon.

An increase in CO2 means an increase in the warming of the Earth. This is known as the green house effect. Now that we know that a forest fire contributes to the release of carbon, which once meeting the atmosphere will turn into CO2, and that this increase in CO2 traps the heat radiating from our earth, we can link this knowledge to global climate change.

The burning of fossil fuels contributes severely to global climate change today. Coal, oil, and gas are called fossil fuels, because they are made of the remains of beings from long ago. Our civilization has for years depended on fossil fuel burning for everything from heating or cooling our houses, to generating electricity and making trains, cars, ships, and planes go. Like Carl Sagan stated in his book Billions and Billions, we are "...like some ghastly cannibal cult, we subsist on dead bodies of our ancestors and distant relatives ruins."

If the Earth heats up significantly, the oceans will absorb more heat energy, which may make hurricanes and typhoons more common. Scientists are also concerned that global warming will also cause a change in ocean current patterns. Such a change could affect the world's weather resulting in regions that have more rain than normal, while others may have less. Severe flooding could occur in some regions at the same time that droughts devastate other regions.

The data that is collected for this project will help researchers understand a greater picture: How is carbon storage in a forest ecosystem influencing atmospheric carbon levels? And eventually, a more specific problem, how do forest fires contribute to the reintroduction of carbon to a regenerating ecosystem?

Methods

Data was collected throughout a period of eight days. The object of day one was to designate the two sites that were being compared also described as the site preparation. Once obtaining the measurements of 42.5m squared, data collection was started.

Daily data collection included measurements of (1) temperature: air, topsoil, and 7cm down into the soil, (2) wind speed and direction, (3) sun intensity and (4) cloud cover. Other data was collected on specific days. This data includes analysis of (1) topography, (2) elevation, (3) soil moisture, (4) soil composition/depth, (5) soil ph and (6) tree root coverage. Drawings and maps of the plots were also created for a landscape survey and vertical survey.

To calculate the amount of carbon storage, initial purposes stated that soil and trees were to be examined.* To measure the carbon stored in the soil, first samples of soil were collected at the center of each site at (1) topsoil (2) 5cm down (3) 10cm down (4) 15cm down and (5) 30cm down. One of the hypotheses that corresponded to the study was that the rate of accumulation of carbon in live trees was greatest in the areas where the trees typically had the fastest volume growth. Hence tree heights and circumferences played a role in the amount of carbon stored and were calculated as well as the type of tree.

Tree height was supplemented by (1) measuring the diameter of the tree, (2) measuring the distance of the person who was measuring, to the tree, (3) measuring an angle of siting by using an astrolabe and (4) by using the height of the person measuring the tree. After obtaining these measurements, the numbers were applied to this equation:

Site preparation is important to mark because it established what plots were to be researched. It is also important to mark a territory so that future scientists could go to the same plots and undergo the same procedures for comparison. The vertical surveys and landscape surveys would allow future scientists to go to the same sights.

*Due to time limitation, there are only tree carbon storage results.

By using the GPS model, elevation, longitude and latitude was found. This data is relevant to identify the sites and to visualize the height of the sites compared to the forest itself. Making records of the topography of each site allows for comparison and identification of the site itself. Topography included the location of rocks and trees or any other distinguished features.

Temperature of the air, floor, and 7cm down, provided a reading for the temperature that enzyme activity can occur in the process of photosynthesis. Also, if the soil temperature resulted to be hot, then it was an indication of how much of the sunís light energy was being stored as heat in the soil. If the temperature of the soil was cool, then one could tell whether the soil was moist enough for proper tree growth.

Observing the cloud coverage gave an understanding of climate change and the role of clouds. Low coverage clouds reflected sun energy and heat while heavy clouds absorbed the heat. It was important to understand how much sunlight was being absorbed to know whether photosynthesis was occurring and it gave a slight idea of the rate in which it was occurring. The sun voltage meter gave accurate readings of how much light energy was being given off and received in the forest floor by the sun.

Soil depth was taken in each of the corners of each plot. Soil depths were considered to measure how deep into the ground was carbon being stored in. Soil composition was observed to classify the kind of ecosystem that was being studied. Soil ph levels were considered to measure the acidity and alkalinity of the soil. By looking at the soil ph one can tell whether it had rained recently and in general what type of soil there is, which helps determine what types of trees can grow.

To measure the amount of carbon stored in trees the first thing that was established was the tree species. The tree species was important because different trees undergo photosynthesis at different rates thus storing different amounts of carbon. Under tree identification, the tree was classified as dominant, co-dominant or suppressed. This is important because it is beneficial to see if taller (more older) trees would store greater amounts of carbon. It was also important to classify them this way because it provided a visual of the tree heights compared to one another. By naming a tree suppressed, one could look at the amount of carbon it stored and if statistics showed a lower amount compared to the dominant trees, one could assume that the dominant and co-dominant trees were getting direct sunlight therefore undergoing more photosynthesis.

Results

Figure 1

Figure 2

Results show that the dominant tree number of both sites is the red oak and in the unburned site, the chestnut oak as well. (Diversity chart) The average tree height of the red oak in site one (unburned) was about 750 cm tall. They were mostly classified as dominant or co-dominant trees.

The average chestnut oak in site one was about 860cm tall, initiating the trees as the most dominant species in height. The average maple was about 342cm tall. Red maple trees in site on were mostly suppressed trees. The average which hazel tree measured 180cm tall.

In site two (burned), results showed that the red oak is the dominant tree in quantity, and in height. The tallest red oak tree in site two measured 1031cm tall, (height chart) appropriately indicating hat the forest was once a mature forest. The average co-dominant tree measured between 446.512cm and 513.565cm tall. Because of the fact that it was a ground fire, all of the suppressed trees were completely burned. Thus there is a lack of diversity in tree height.

Figure 3 shows the general tree height between the two studied plots. By looking at this chart, one can see that for one thing, there are no trees in the burned site under 400cm. This is due to the fact that the fire was a ground fire destroying all the suppressed trees in the area. From this graph, one can also deduce that the plant life inhabiting the unburned site is flourishing as the time passes by. Realizing that since there is diversity in tree height, young trees must be growing while the older trees are living and growing as well makes this conclusion.

Figure 3 also suggests that there are some trees around the same height in each plot, meaning that at one time both these areas where the same in biodiversity and vegetation and as a result of the ground fire, only the tallest trees survived.

Figure 3

Figure 4

This research has concluded that more carbon is stored in the unburned plot than in the burned plot. There is 15% more carbon in kilograms stored in the unburned plot than there is in the burned plot. Possible reasons for this conclusion are that there is more biodiversity in the unburned area than in the burned area. Also more trees were counted in the unburned plot than in the burned plot. Another factor that plays a role is the diameter of each tree. The diameters of the trees in the unburned site were larger than the diameter of the trees in the burned plot.

Discussion

The main objective proposed for this study was to see what effects a forest fire had on the storage of carbon. The results showed that more carbon was stored in the unburned plot than in the burned plot. From this outcome one can infer that a forest fire depletes the amount of carbon that was originally stored in the forest before the fire.

The relationship between a forest and carbon is an imperative relationship that must be understood to its fullest. Forest ecosystems can add to the pool of carbon dioxide in the atmosphere through deforestation, the decomposition of wood products and byproducts, or by the combustion of forestlands. Forests can also reduce the amount of carbon dioxide in the atmosphere through increases in biomass and organic matter accumulation.

In regard, there are many factors that should be taken into account when administrating a study on carbon storage in forest ecosystems. The diversity and classification of trees in addition to the tree heights and diameters are essential factors that should be calculated to quantify the amount of carbon stored in the trees.

If in future years carbon levels have increased in drastic rates, as it is being predicted, then forests will not be able to maintain a healthy balance between the carbon dioxide thatís released and the carbon that is stored. And the burning of forests will just make the matter worst.

Future Research Ideas

Although more carbon is stored in the unburned site, more research is needed to validate these results. Future research ideas include measuring a larger quantity of trees in each site. It would also be beneficial to conduct this experiment under a longer period of time. Long-term studies of these sites could confirm the conclusion that more carbon is stored in an unburned forest ecosystem than in a burned area.

There are valid proposals about studying the amount of carbon stored in aquatic ecosystems since it is known that oceans store large and significant amounts of carbon. These studies would also take place at Black rock. In addition, being that there is a deer exclusion at Black Rock Forest, it would be appropriate to study the effects that the deer population has on the amount of carbon stored in the trees that surround them. These proposed studies and hopefully others that will be anticipated in the years to come will bring us closer to understanding the carbon flux and maybe then might science be able to mitigate the effects of global climate change.